1. Field of the Invention
The present invention relates to a system and a method for controlling a fuel injection to an engine. More particularly, the present invention relates to a system and a method for controlling the number of pilot injections which reduces combustion noise and improves fuel economy by deciding the actual number of the pilot injections based on a change amount of a driving condition and injecting a fuel according to the actual number of the pilot injections in a case of acceleration.
2. Description of the Related Art
It is generally known that a diesel vehicle, compared with a gasoline vehicle, generates more soot and smoke and larger vibration/noise. A diesel particulate filter (DPF) is mounted at the diesel vehicle so as to reduce such soot and smoke, and multi-pilot injection is introduced in the diesel vehicle so as to reduce vibration/noise. In addition, various means for improving combustion is being introduced in the diesel vehicle.
Particularly, rigidity of the vehicle is strengthened and sound blocking and absorbing material is used in hardware aspect, and fuel injection factors such as injection pressure, injection timing, and fuel amount are determined according to engine speed and load, the fuel injection factors are corrected according to environmental variables (e.g., outer temperature, atmospheric pressure, and coolant temperature), and fuel injection is performed based on the corrected fuel injection factors in software aspect in order to reduce combustion noise of the diesel vehicle. In addition, the number of pilot injections is increased and increasing rate of combustion pressure is reduced so as to reduce combustion noise.
FIG. 4 is a graph showing combustion pressure to crank angle in a case that a fuel is injected through a main injection and through main injection/pilot injection.
A bold line represents a case where a fuel is injected only through a main injection, and a fine line represents a case where the fuel is injected through main injection/pilot injection in FIG. 4.
The pilot injection creates combustion atmosphere (temperature in a combustion chamber is raised so as to improve mixture of fuel and air) before the main injection, and reduces ignition delay and the increasing rate of the combustion pressure caused by the main injection.
As shown in FIG. 4, if the fuel is injected through the main injection and the pilot injection, compared with a case where the fuel is injected only through the main injection, the combustion pressure, first derivative of the combustion pressure to time, and second derivative of the combustion pressure to time become smaller. As known to a person of an ordinary skill in the art, the combustion pressure influences the combustion noise at a low frequency region and first and second derivatives of the combustion pressure to time influence the combustion noise at high frequency region. Therefore, reducing the combustion pressure and first and second derivatives of the combustion pressure to time is very important for reducing the combustion noise, and this will be achieved by increasing the number of pilot injections.
Generally, the combustion noise occurs mainly when an initial acceleration. According to conventional arts, the number of pilot injections is decided according to a driving condition of an engine such as a throttle opening and an engine speed. However, a change amount of the driving condition of the engine is not reflected in the number of pilot injections. In addition, the number of pilot injections required at the initial acceleration should be different from that required at an end of acceleration under the same driving condition of the engine. That is, the number of pilot injections should be increased so as to create the combustion atmosphere at the initial acceleration, but the number of pilot injections should be reduced so as to enhance fuel economy at the end of acceleration.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.